1. Field of the Invention
The present invention relates to an inside diameter measuring method and apparatus. More particularly, it relates to an inside diameter measuring method and apparatus for measuring an inside diameter of a minute cylindrical work such as ferrule and injection.
2. Description of the Related Art
When the inside diameter of a minute cylindrical work such as a ferrule is measured, measurement has so far been made by inserting a pin gage of a predetermined size into the inner peripheral portion of the work by a person who makes measurement. In the measurement using the pin gage, however, it is necessary for the measurer to manually make measurement one work after another, which presents a drawback of requiring much labor. Also, the conventional measuring method has a drawback of poor accuracy because of manual operation.
The inventor has proposed a method in which compressed air is supplied into the inner peripheral portion of work, and a change of back pressure is detected to measure the inside diameter of work, in Japanese Patent Application No. 2001-40669 corresponding to International Patent Application No. PCT/JP02/01086 (which was, at the time the present invention was made, not published, not publically known, and assigned to the same assignee to which the present invention was subject to an obligation of assignment). This method has an advantage that because compressed air is merely supplied to the work, measurement can be made in a short period of time, and also because of no wear, stable measurement can always be made even after long-term use.
When many works are measured at one time using the above-described method, however, if individual works have variations in length, different back pressures are detected even if the works have the same inside diameter. As a result, there arises a drawback of variations in measured value.
The present invention has been achieved in view of the above situation, and accordingly an object thereof is to provide an inside diameter measuring method and apparatus capable of making accurate measurement even if a length of work varies.
To attain the above object, the present invention is directed to an inside diameter measuring method of measuring an inside diameter of a cylindrical work by supplying compressed air from one end of the work and by detecting the back pressure of the compressed air, wherein a correction amount of measured value of the inside diameter according to the length of the work is obtained in advance by determining a change of measured value of the inside diameter with respect to a change of length of the work, whereby the measured value of the inside diameter is corrected according to the length of the work.
The present invention is also directed to an inside diameter measuring apparatus which measures an inside diameter of a cylindrical work by supplying compressed air from one end of the work and by detecting a back pressure of the compressed air, comprising: a length measuring device which measures a length of the work; a storage device which stores a correction amount of measured value of the inside diameter according to the length of the work; and a correcting device which corrects a measured inside diameter of the work based on the length of the work measured by the length measuring device and the correction amount stored in the storage device.
According to the present invention, the measured value of the inside diameter is corrected according to the length of the work by obtaining a correction amount of measured value of the inside diameter according to the length of the work in advance. Thereby, accurate measurement can be made even in the case where a plurality of works having a varied length are measured.